refactor(provider): use local settings for current provider selection

Complete the device-level settings separation for cloud sync support.

Backend changes:
- Modify switch() to update both local settings and database is_current
- Modify current() to read from local settings first, fallback to database
- Rename sync_current_from_db() to sync_current_to_live()
- Update tray menu to read current provider from local settings

Frontend changes:
- Update Settings interface: remove legacy fields (customEndpoints*, security)
- Add currentProviderClaude/Codex/Gemini fields
- Update settings schema accordingly

Test fixes:
- Update Gemini security tests to check ~/.gemini/settings.json
  instead of ~/.cc-switch/settings.json (security field was never
  stored in CC Switch settings)

This ensures each device maintains its own current provider selection
independently when database is synced across devices.

src-tauri/src/lib.rs

@@ -220,9 +220,16 @@ fn create_tray_menu(
     for section in TRAY_SECTIONS.iter() {
         let app_type_str = section.app_type.as_str();
         let providers = app_state.db.get_all_providers(app_type_str)?;
-        let current_id = app_state
-            .db
-            .get_current_provider(app_type_str)?
+
+        // 优先从本地 settings 读取当前供应商，fallback 到数据库
+        let current_id = crate::settings::get_current_provider(&section.app_type)
+            .or_else(|| {
+                app_state
+                    .db
+                    .get_current_provider(app_type_str)
+                    .ok()
+                    .flatten()
+            })
             .unwrap_or_default();
 
         let manager = crate::provider::ProviderManager {